Testing of wheels and hubs for automobiles and trucks is used extensively for both development purposes and for quality control. The methods of testing heretofore have often been slow, inefficient, costly and not always exactly correlate with the fatigue life of the wheel or a hub in the field.
The testing of a wheel or hub heretofore has generally required the wheel to be rotated a large number of time. The total life test of the wheel and hub is generally in the order of a quarter of a million cycles and normally would take several weeks or months to test under normal conditions. This problem can not be solved simply by speeding up the process, such as rotating the wheel faster, because it was found that there are practical limits due to tire wear, bearing wear, excessive heat, excessive horse power required, and other things which limit the speed at which the wheel can be rotated. Also, increasing the speed of the wheel to the maximum rate possible would require a machine of gigantic proportions both in size, weight, horsepower and the like.
Heretofore, in testing the wheels and hubs, it was believed that the rotation of the wheel contributed to a major part of the stresses produced in the wheel during testing. In developing the present invention, however, it was discovered that the rotation or cyclic part of the test was not a large contributor to the total strain levels on the wheel as the wheel rotated over rough surfaces. It was discovered that the random type input, such as resulting from holes and bumps in the road, turned out to be a much larger contributor than the steady state load which heretofore was associated with the rotation of the wheel.